This invention relates to the thermal transfer of a black matrix onto a receptor and related thermal transfer donor sheets and products made therefrom. In particular, the invention relates to the thermal transfer of a black matrix onto a receptor using a thermal transfer donor sheet having a donor layer that includes carbon black.
Black matrix coatings are used in many display applications to absorb ambient light and improve contrast. The black matrix is formed around individual pixels or light emitters of the display. In many liquid crystal displays (LCDs), the black matrix is a 0.1 to 0.2 xcexcm coating of black chromium oxide on a display substrate. Black chromium oxide is typically sputtered onto the display substrate and is a relatively expensive process. In addition, the black chromium oxide typically forms a metallic surface with higher than desired reflectivity (and correspondingly reduced contrast). Furthermore, there are environmental and health concerns associated with chromium.
Resin black matrix (a pigment in a resin matrix) has been suggested as an alternative to black chromium oxide. The resin black matrix is coated onto the display substrate and then patterned using photolithography. To achieve a high optical density in a thin resin black matrix coating, it is typically necessary to use relatively high pigment loadings. This makes photolithography difficult because the patterning light (e.g., ultraviolet (UV) light) typically does not penetrate well into coatings with high optical densities. In addition, coatings with high levels of pigment have less resin. Because resin is the component of a coating that is etched, high optical density coatings (i.e., coatings with high pigment content) may not etch cleanly.
Generally, the present invention relates to the formation, by thermal transfer, of a black matrix on a receptor substrate for use, for example, in a display application. In particular, the present invention is directed to methods of making a color filter black matrix and/or a TFT (thin film transistor) black matrix, as well as the thermal transfer elements suitable for use in the methods, and the articles formed by the methods.
One embodiment is an optical display that includes a substrate, pixel elements disposed on the substrate, and a black matrix disposed between the pixel elements. Each of the pixel elements includes at least one electrically-conducting element to operate the pixel element. The black matrix has an optical density sufficient to provide optical contrast between the adjacent pixel elements, a resistivity that substantially prevents cross-talk between the electrically-conducting elements of adjacent pixel elements, and a thickness to maintain substantial planarity with at least a portion of adjacent electrically-conducting elements.
Another embodiment is a thermal transfer element for transferring a black matrix to a receptor to separate adjacent active devices. The thermal transfer element includes a substrate, a light-to-heat conversion layer, and a transfer layer. The transfer layer includes carbon black and is typically configured and arranged to provide, when transferred to a receptor, a black matrix having an average resistivity of at least 1xc3x971010 ohm-cm.
Yet another embodiment is a thermal transfer element for transferring a black matrix to a receptor to separate adjacent active devices. The thermal transfer element includes a substrate, a light-to-heat conversion layer, and a transfer layer. The transfer layer includes carbon black and is typically configured and arranged to provide, when transferred to a receptor, a black matrix having an optical density of at least 2.4.
A further embodiment is a method of forming a display device having pixel elements that each include an electrically-conducting element to operate the pixel element. A light-to-heat conversion layer is formed over a donor substrate. A black matrix transfer layer is formed over the light-to-heat conversion layer. The black matrix transfer layer is brought into contact with a substrate of the display device. The light-to-heat conversion layer is selectively irradiated, according to a pattern, with light having at least one wavelength that the light-to-heat conversion layer can convert to heat energy. A portion of the black matrix transfer layer is then thermally transferred, according to the pattern, to the substrate of the display device to form a black matrix defining a plurality of pixel elements. The black matrix has an optical density sufficient to provide optical contrast between adjacent pixel elements, a resistivity that substantially prevents cross-talk between the electrically-conducting elements of adjacent pixel elements, and a thickness to maintain substantial planarity with at least a portion of adjacent electrically-conducting elements. An electrically-conducting element is formed for each pixel element on the substrate of the display device. The black matrix separates adjacent electrically-conducting elements.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.